1. Field of the Invention
The present invention relates to a timing generator provided for an electronic endoscope unit, which generates pulse signals for image signal sampling.
2. Description of the Related Art
In recent medical practice, electronic endoscopes have been widely used for medical examinations. An electronic endoscope is utilized with an image-signal processing unit and image-indicating device, such as a TV monitor. The electronic endoscope is connected to the image-signal processing unit and an image captured at the end of the flexible conduit of the endoscope is fed to the image indicating device through the image-signal processing unit and displayed. Various types of electronic endoscopes are utilized for examinations. However, it is a waste of space and money to have an image-signal processing unit for each electronic endoscope. It is better for an image-signal processing unit to be shared among several electronic endoscopes, in which signal processing is common.
An imaging device, such as a CCD (charged coupled device), is attached to the distal end of a flexible conduit of an electronic endoscope, which is inserted into a body cavity or hollow organ, hence, the distal end of the endoscope is required to be miniature. Therefore, a CCD driver, which feeds driving signals to the CCD, or a CDS (correlated double sampling) circuit, which samples input-image-signals from the CCD and holds an output value of the most recent sampling, are conventionally disposed in the image-signal processing unit, which is externally prepared for the endoscope. The delay time between the output of the driving signals from the CCD driver and the input of image signals, which are detected by the foregoing driving signals, to the CDS circuit, relates to the length of the endoscope. Lengths of electronic endoscopes vary from a meter or less to several meters, thus the delay time for signal transmission turns out to be considerable for image-signal processing. Among the electronic endoscopes that share one image-signal processing unit, the length of the flexible conduit of the endoscopes varies according to the use of the endoscope. The amount of time required for sampling the image signals from the CCD, at the CDS, depends on the length of the flexible conduit of the endoscope. Therefore, in a conventional image-signal processing unit, delay lines that correspond to electronic endoscopes of which the length of each flexible conduit is different, are provided for executing appropriate sampling and holding for image signals. However, in the case of sharing of the image-signal processing unit among numerous electronic endoscopes that have dissimilar lengths of flexible conduit, numerous delay lines are required for the image-signal processing unit. Further operators need to switch the delay lines when they change the electronic endoscopes connected to the image-signal processing unit. So that the construction of the image-signal processing unit and its operations are cumbersome.
In Japanese Patent No. 2790948, an electronic endoscope unit is described that is provided a CDS circuit and a circuit which can change phase between a clamp pulse and a sample pulse fed to the CDS circuit. These circuits are inside the operating handle or a connecting part of an electronic endoscope, which is used to connect the electronic endoscope to an image-signal processing unit. The phase between the clamp pulse and sample pulse is adjusted by controlling the time constant of the R-C circuit that comprises a potentiometer. However, as for miniaturizing a circuit, a circuit comprising a potentiometer is at a disadvantage. Further, in an analog circuit, devices should be placed mutually close together. Therefore, in the disclosed electronic endoscope unit, the potentiometer, CCD driver and CDS circuit are required to be placed integrally in close formation. Further, in order to facilitate the operation of the phase adjustment, the potentiometer should be disposed at an accessible position and also a cover for the potentiometer should be formed in a structure that can be easily detached from the body, when an adjustment is required. However, since the electronic endoscope is frequently syringed, the above disposition and structure is inferior from the aspect of the waterproofing of the electrical devices, i.e. the potentiometer, CCD driver, and CDS circuit. Further, the above problems, such as the miniaturizing difficulty of the circuit, the disposition of the potentiometer, and the structure of the cover, also enlarge the size and limit the form of the operating handle of the endoscope. Since in the design of the operating handle, manipulation is a significant factor, thus the above problems are serious. Furthermore, since the size of the adjustment knob of the potentiometer is small, operation of the knob, to adjust the phase, is quite difficult.
Therefore, an object of the present invention is to provide a miniaturized sampling pulse generator for an electronic endoscope, which has high flexibility in circuit arrangement and ease of phase adjustment.
According to the present invention, a sampling pulse generator utilized in an electronic endoscope with an imaging device is provided that comprises a sampling circuit, driving pulse generating processor, clock pulse generator, shift counter, first switch group, second switch group, and switch setting processor.
The sampling circuit samples image signals obtained by the image capturing device and the driving pulse generating processor generates driving pulses for the imaging device. The clock pulse generator cyclically generates clock pulses and the pulses are cyclically counted within a predetermined number by the shift counter. The shift counter comprises a predetermined number of output terminals and each of the count numbers, within the predetermined number, corresponds to the output terminals by one-to-one. Further, a signal is only output to a terminal corresponding to a current count number. The first and second switch group comprises switches connected to each of the output terminals. The switch setting processor sets the on-off states of the switches in the first and second switch groups. Furthermore, the driving pulse generating processor generates the driving pulses by signals from the output terminals of the shift counter and at least two types of sample pulses that control the sampling circuit are generated by signals from the first and second switch groups. The switch setting processor sets the on-off states of the first and second switch groups.
The switch setting processor may comprise a recording medium that records data relating to the on-off states for the first and second switch groups. In this case, the on-off states of the first and second switch groups are set in accordance with the data recorded in the recording medium.
The sampling pulse generator may further comprise a recording processor that sets the data and the recording processor may be controlled by instructions from a computer connected to the electronic endoscope. For example, the recording medium is EEPROM.
Preferably, a correlated double sampling circuit is utilized as the sampling circuit and the two types of sample pulses are clamp pulses and sample-hold pulses. In this case, the clamp pulse is output from the first switch group and the sample-hold pulse is output from the second switch group.
Preferably, the driving pulses are generated by logical sum of signals fed from predetermined terminals of the output terminals and these terminals correspond to consecutive count numbers of the cyclic count within the predetermined number.
For example, a CCD is utilized as the imaging device and the driving pulses comprise a CCD horizontal-register transfer clock. In this case, the CCD horizontal-register transfer clock is generated by signals from the predetermined terminals and the number of the predetermined terminals corresponds to half of the predetermined number.
Further, the switch setting processor may comprise a third switch group that sets the on-off states of the first and second switch groups. In this case, the on-off states of the first and second switch groups are set in accordance with binary data produced by switches in the third switch group.